شاید برای نخستین بار، توجهِ یک تحقیق بر روی این نظریه علمی استوار است که خوردن گیاهان و گوشت پخته شده، سهم اصلی در بزرگ شدن مغز انسان داشته است. بر اساس تحقیق فوق، مغز انسان معاصر، حدود ۲۰ درصد از کالری  بدن را مصرف می کند و این مقدار دو برابر اندازه ای است که سایر پستانداران نظیر گوریل لازم دارند.   .

در تحقیق مورد نظر ضمن محاسبات دقیق ریاضی، مقدار انرژی ناشی از فعالیت عصب های مغزی چندین پستاندار نزدیک به انسان محاسبه شده است. محققین پی بردند همه  آنهایی که بدن های بزرگتر دارند از مغز بزرگتر نیز برخوردار هستند ولی انسان، استثنایی را ایجاد کرده است که ناشی از بزرگی بیش از حد مغز وی نسبت به بدنش است.

 گوریل ها با آنکه سه برابر هیکل انسان وزن دارند ولی از مغز کوچکتری برخوردار هستند. گوریل ها ولی گیاهخوار هستند و برای آنکه انرژی روزانه لازم را تهیه کنند ناچارند ساعت های متمادی روز را صرف خوردن گیاهان خام کنند.

بر طبق محاسبات تیم دانشمندان برزیلی به رهبری دکتر متخصصِ عصب Suzana Herculano-Houzel از دانشگاه دولتی ریودوژانیرو، گوریل ها برای تامین انرژی مغزی برابر با انسان، به ۷۳۳ کالری بیشتر احتیاج دارند. این مقدار در زندگی طبیعی آنها مساوی است با صرف ۲ ساعت بیشتر از وقت روزانه برای خوردن گیاهان است. این در حالی است که گوریل ها، به خودی خود ۸۰ درصد از ۱۲ ساعت روشن در روز را صرف خوردن گیاهان می کنند.

محققین معتقدند انسان اولیه نیز اصلا شرائط لازم امنیتی و فیزیکی برای صرف بیشتر از ۹ ساعت از روز برای کسب انرژی را نداشته است. دکتر سوزانا هرکولانا بر اساس اندازه گیری های دقیق، از جمله محاسبه مصرف دقیق مقدار انرژی که صرف عصب های مغزی می شود به این نتیجه رسیده است که انسان اولیه ناگزیر بود که به خوردن و پختن گوشت پناه ببرد.

 او می افزاید: « با وجود آنکه برای انسان معاصر، امکان ادامه حیات از طریق مصرف گیاهان امکان پذیر است ولی وقتی انسان های اولیه با هیکل های کوچک ولی مغز بزرگتر پا به عرصه وجود گذاشتند اتکای تنها به گیاهان خام برای تامین انرژی، امکان ناپذیر بوده است. دستیابی به گیاه و گوشت پخته شده باعث شده است که مواد آلی و غذایی بیشتری در اختیار انسان قرار بگیرد و مشکل مغز پر مصرفش را حل کند.»

Sorry, vegans: Eating meat and cooking food is how humans got their big brains

Researchers from Brazil, led by Suzana Herculano-Houzel, a neuroscientist at the Federal University of Rio de Janeiro

Vegetarian, vegan and raw diets can be healthful, probably far more healthful than the typical American diet. But to call these diets “natural” for humans is a bit of a stretch in terms of evolution, according to two recent studies.

Eating meat and cooking food made us human, the studies suggest, enabling the brains of our prehuman ancestors to grow dramatically over a few million years.

Although this isn’t the first such assertion from archaeologists and evolutionary biologists, the new studies demonstrate that it would have been biologically implausible for humans to evolve such a large brain on a raw, vegan diet and that meat-eating was a crucial element of human evolution at least a million years before the dawn of humankind.

At the core of this research is the understanding that the modern human brain consumes 20 percent of the body’s energy at rest, twice that of other primates. Meat and cooked foods were needed to provide the necessary calorie boost to feed a growing brain.

One study, published last month in the Proceedings of the National Academy of Sciences, examined the brain size of several primates. For the most part, larger bodies have larger brains across species. Yet humans have exceptionally large, neuron-rich brains for our body size, while gorillas — three times as massive as humans — have smaller brains with one-third the neurons. Why?

The answer, it seems, is the gorillas’ raw, vegan diet (devoid of animal protein), which requires hours upon hours of eating to provide enough calories to support their mass.

Researchers from Brazil, led by Suzana Herculano-Houzel, a neuroscientist at the Federal University of Rio de Janeiro, calculated that adding neurons to the primate brain comes at a fixed cost of approximately six calories per billion neurons.

For gorillas to evolve a humanlike brain, they would need an additional 733 calories a day, which would require two more hours of feeding, the authors wrote. A gorilla already spends as much as 80 percent of the tropics’ 12 hours of daylight eating.

Similarly, early humans eating only raw vegetation would have needed to munch for more than nine hours a day to consume enough calories, the researchers calculated. Thus, a raw, vegan diet would have been unlikely, given the danger and other difficulties of gathering so much food.

Cooking makes more foods edible year-round and releases more nutrients and calories from both vegetables and meat, Herculano-Houzel said.

“The bottom line is, it is certainly possible to survive on an exclusively raw diet in our modern day, but it was most likely impossible to survive on an exclusively raw diet when our species appeared,” Herculano-Houzel told LiveScience.

The study puts an upper limit on how big a brain is able to grow while on a premodern raw, vegan diet. But the researchers could not determine when daily cooking began. Was it about 250,000 years ago, when humans were nearly fully evolved with big brains, which is supported by archaeological findings? Or was it about 800,000 years ago, when prehumans began their most dramatic brain-growth spurt, an era for which there is little archaeological evidence of controlled fires for cooking?

If cooking wasn’t routine before the dawn of modern humans, eating meat certainly was.

The second study, published in October the journal PLoS ONE, examined the remains of a prehuman toddler who died from malnutrition about 1.5 million years ago. Shards of a skull found in modern-day Tanzania reveal that the child had porotic hyperostosis, a type of spongy bone growth associated with low levels of dietary iron and vitamins B₉ and B₁₂, the result of a diet lacking animal products in a species that requires them.

The child was around the weaning age. So either the child’s mother’s breast milk lacked key nutrients or the child himself did not consume enough nutrients directly from meat or eggs.

Either way, the finding implies that meat must have been an integral, and not sporadic, element of the prehuman diet more than 1 million years ago, said the study’s lead author, Manuel Dominguez-Rodrigo, an archaeologist at Complutense University in Madrid.

This supports the theory that meat fueled human brain evolution because meat — from arachnids to zebras — was plentiful on the African savanna, where humans evolved, and is the best package of calories, proteins, fats and Vitamin B₁₂ needed for brain growth and maintenance.

“Carnivore animals, whether terrestrial or aquatic, are bigger-brained than herbivores,” Dominguez-Rodrigo told LiveScience. He added that “there is no [traditional] society that live as vegans,” essentially because it wouldn’t be possible to get Vitamin B₁₂, which is only available in animal products.

Both sets of researchers said their conclusion — that cooked food and meat were necessary for human brain development — is not a statement of how the human diet must have been but rather how it likely was in order to make humans “human.”

With supermarkets and refrigeration, humans today can and increasingly do eat a vegetarian or vegan diet year-round. And given the amount of heart-stopping saturated fats in factory-produced animal products, a plant-based diet can be more healthful.

Yet both extremes of the meat argument — the unapologetic meat-eater and the raw vegan — should remember that few of today’s so-called natural foods were around as little as a few hundred years ago, from the modern invention called corn-fed beef to genetically altered strains of Queen Anne’s lace called the carrot.

There are many reasons to go vegetarian, go vegan and even go raw, but evolution isn’t one of them.

Wanjek is the author of “Hey, Einstein!,” a comical nature-vs.-nurture tale about raising clones of Albert Einstein in less than ideal settings. His column, Bad Medicine, appears regularly on LiveScience.